Switching scheme



Get. 8, 1940. H. R, SHAW SWITCHING SCHEME Filed Ndv. 2, 193a AMPLIFIERCOMMON TALK AND LISTEN Inventor: Huber-t R. Shaw HI Attorney.

Patented a. a, 1940 PATENT OFFICE swrrcnmo SCHEME Hubert R. Shaw,Bridgeport, Conn., assignor to General Electric Company, a. corporationof New York Application November 2, 1938, Serial No. 238,415 3 Claims.(01. 179-1) My invention relates to communication systems andparticularly to such systems as are used for interofiice communication,public address, etc.

In such systems commonly an amplifier is em- 5 ployed which isalternately reversed in its connections to amplify signals from eitherof two signal stations and to transmit the amplified signals to theother station.

One object of my invention is to provide such a system having means toprevent regeneration of said amplifier due .to any coupling betweenconductors which are connected respectively to the input and output ofsaid amplifier and which may be close to each other as in twisted linesin any practical installation of the equipment.

Another object of my invention relates to such a system employing suchmeans for preventing regeneration in which means are also employed toprevent extraneous noises at the location of any station from beingreproduced at a different station when the system is not in use.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which the single figure represents anembodiment of my invention.

Referring to the drawing I have shown at I a central station, at 2, 3,4, and 5 a number of outlying stations, and at 6 an amplifier, togetherwith 85 means whereby the operator at station I may call any of stations2, 3, 4, and 5 through said amplifier, and whereby he may be calledthrough said amplifier from any of said stations 2, 3, 4, and 5. Thismeans comprises a plurality of switches including a talk-listen switch Ilocated at the central station I and also a talk-listen switch 8 locatedat each of the other stations.

The talk-listen switch I at the central station I comprises a pluralityof stationary contacts 9,

III, II, l2, l3, I4, and I5, mounted upon a stator l6, and a pluralityof conducting segments 20, 2|, and 22, mounted upon a rotor 23. Thisrotor may be a suitable non-conducting disk upon which the 50 segmentsare mounted and which is rotated about an axis by means of a handle 24movable between two positions as shown in the drawing. The talklistenswitches 8 of the stations 2, 3, 4, and 5 are simple double-throwswitches which are arranged 55 to connect the loud speaker between thecommon conductor 21 and either of two conductors 25 or 26 extending toeach'station.

The stations I, 2, 3, 4, and 5 may all comprise simple loud speakerspreferably of the dynamic type having permanent magnets 0r field coils.One side of all these loud speakers is connected to a common, or groundconductor 21, and to one side of the input transformer 28 of amplifier 6and to one side of the output transformer 29, of amplifier G, therespective switches l and 8 being shown on the opposite side of thevarious circuits.

At 30 is a selector switch which may be of the ordinary so-called Yaxleyconstruction comprising a plurality of wafers, each wafer having anumber of stationary contacts and rotating conducting segmentscooperating therewith, one wafer 3| being provided for conductors 25extending to the different outlying stations, and. the other wafer.32being provided for conductors 26 extending to the different outlyingstations; By means of these switches as will presently be explained, anyone, or all of-the outlying stations 2, 3, 4, and 5 may be connected bythe operator at station I for communication with the central station I.

The rotor of the switch 30 is also provided with a member 35 which inone extreme position of the switch engages a switch member 36 arrangedin the power supply circuit 31 for the amplifier 3,

thereby interrupting the supply of power to that ampl er.

Having thus indicated the general nature of the equipment to which myinvention pertains I shall -now describe ,the various circuits employedin greater detail by reference to its operation. It will be observedthat with the switches in the position shown the loud speaker I isconnected directly across the secondary winding of transformer 29; thiscircuit comprises loud speaker I, stationary contact i5, segment 22,stationary contact I4, secondary winding of transformer 29 and ground,or common conductor 21, back to the loud speaker.

It will also be observed that with the switches in the position shown,although station i is connected for listening, no currents generated byreason of noise in the localities of stations 2, 3, 4, and 5 orotherwise, are transmitted to the input of the amplifier I foramplification thereby, and hence produce no disturbance in the stationI. This'is by reason of the fact that the circuit of conductors 26 forstations 3, 4, and 5 are all open at segment 38 of water 32 of switch30, and the circuit of conductor 26 for station 2 is also open atsegment 2| of switch I.

With the switch 30 in the position shown the operator at stations 3, 4,and is incapable of callingstation; I The operator at station 2,however, may call station I by moving switch 8 to the left andspeakinginto his loud speaker. The circuit for the loud speaker ofstation 2 extends from ground through ground conductor 21, loud speaker2, switch 8 in its left-hand-position, conductor 25 of station 2,segment 33 of switch 30, contact 40, conductor 4|, stationary contactII, segment 20, and stationary contact III of switch I, conductor 42 andprimary winding of input transformer 28 to ground. These currents are ofcourse amplified by amplifier 5 and supplied to station I.

The. operator at station I may now answer the call by operating hisswitch Iv to the opposite, or talk, position which is the dotted lineposition of handle 24 shown in the drawing. In this position theconducting segments 20, 2I, and 22 are rotated counterclockwise by thedistance equal to the space between two adjacent contacts. In thisposition conductor 43 of station I is connected through stationarycontacts I4, segment 22 and stationary contact I3 to conductor 4| andthence through stationary contact 40, segment 38 and stationary contact44 of switch 3l'to conductor 25 of station 2 with which conductor switch8 is now in engagement. The output currents from the amplifier 5 arethus transmitted to the loud speaker 2. At the same time loud speaker Iis connected to the input of the amplifier through stationary contact 9,segment 20 and contact ID of switch I, and conductor 42 to the primarywinding of transformer 28. Thus any words spoken by the operator atstation I are heard by the operator at station 2.

During the subsequent conversation it is necessary for the operator atstation I to alternate switch I between its talk and listen positions ashe alternately talks and listens. The switch 8 in the outlying station,however, may remain in its left-hand position throughout theconversation.

If, with the equipment in the position shown in the drawing, theoperator at station I desires to call any of the stations 2, 3, 4, and 5he operates the switch 30 to the position corresponding to the stationto be called and the switch 24 to the talk position and then speaks'into the loud speaker. His loud speaker is then connected to the inputof the transformer through stationary contacts 9 and III of switch I.The output of the amplifier is connected through conductor 43,stationary contact I4, segment 22, and contact I3 of switch I, thencethrough stationary contact II, segment 2I and contact I2 of switch 1,conductor 45, stationary contact 46 and segment.

and that one of the other stationary contacts with which it may be inengagement of switch '32 to conductor 26 of the called station. Thus thewords spoken into the loud speaker I are heard by the operator at thecalled station.

The operator at the called station then moves his switch 8 to the leftand answers into his microphone.

It will .be seen that the loud speaker at station by moving its switch Ito the talk position. In this position the subsequent conversation maybe carried on without further manipulation of switch 8.

All of stations 2, 3, 4, and 5 are connected to the system by means ofswitches 3I and 32 in exactly the same way as that shown on the drawingfor station 2 when switches 3| and 32 are moved in the counterclockwisedirection to corresponding positions. If this switch be moved in thecounterclockwise direction through the space of one contact then all ofthese stations are connected together; that is, all of the conductors 25of the various stations are connected together by segment 49 of switch3I and all conductors 26 are connected together by segment 38 of switch32, all of conductors 25 are then also connected to switch I throughsegment 39, stationary contact 40, and conductor M and similarly all ofconductors 25 are connected to switch I through segment 41, contact 46and conductor 45. Thus, if the operator at station I operates his switchto the talk position and speaks into the loud speaker his words arereproduced at all of the outlying stations. Hall of the operators at theoutlying stations operate their switches to the left they may all talkwith the central station as in conference telephony.

The conductors 25, 26, and 21 which exten to the outlying stations may,of course, be twisted together or in cable form. With the circuitsarranged as described, no regeneration of the amplifier is produced byreason of conductors connected to the input and outlet circuits butwhich are twisted together, or lie in proximity to each other,throughout any considerable length extending to a distant station. Theswitch I and the conductors 42 and 43 as well as loud speaker I may allbe arranged within the housing of amplifier 5 and thus there is noappreciable coupling between the output and input circuit of theamplifier in these conductors.

All of conductors 25 are connected to conductor 21 at their remote endsby resistors 45. These resistors have such a value as to load the lineand reduce pick up of noise and disturbing voltages therein.

While I have shown particular embodiments of my invention it will, ofcourse, be understood that I do not wish to be limited thereto, sincediffer-' ent arrangements both in the circuit arrangement and theinstrumentalities employed may be made without departing from the spiritand scope of my invention. I, therefore, contemplate by the appendedl-aims to cover any such modifications as fall within the true spiritand scope of my invention.

What I claim as new anddesire to secure by Letters Patent of the UnitedStates is:

1. In combination, a pair of intercommunicating stations, an amplifierat one of said stations, means to connect said amplifier fortransmission from either of said. stations to the other, said meanscomprising double-throw switches in each station, each ofsaid switchesbeing arranged in one position to' connect the respective station to oneconductor for talking thereover and in the other position to connect itto another conductor for listening thereover, said conductors connectingsaid amplifier with said switches, and switching means to isolate anyconductor extending between said stations connected to the input of saidamplifier from any conductor extending between said stations connectedto the output of said amplifier thereby to avoid feed-back from theoutput of said amplifier to the input thereof.

2. In combination a pair of intercommunicating stations, an amplifier,common, talk and listen conductors, extending from said amplifier toeach of said stations, the listen conductor of one station beingconnected to the output of said amplifier and the listen conductor ofthe other station being open circuited at said one station, and the talkconductors being connected to the input of said amplifier, each stationbeing normally connected between the respective common and listenconductors and having switching means to disconnect it therefrom and toconnect it between its common and talk conductors, and means in said onestation to connect the output of said amplifier to the listen conductorof the other station whereby regeneration of said amplifier is notproduced by reason of coupling between the talk and listen conductors ofsaid other station.

3. In combination a pair of intercommunicating stations, threeconductors joining said stations, an amplifier in one of said stations,said 5 one station being normally connected across the output of saidamplifierand the other station being normally connected between two ofsaid conductors, one of which is grounded and the other of which isdisconnected from said ampli- 10 fier, means to connect said otherstation between said grounded conductor and a third of said threeconductors, said third conductor being connected to the input of saidamplifier, and means at the one station to connect that station across15 the input to said amplifier and to connect the output of saidamplifier to said other of said three conductors.

HUBERT R. SHAW.

